The present invention relates to fuel injection pumps for internal combustion engines.
More particularly it relates to a fuel injection pump for internal combustion engines having a pump plunger which defines a pump work space connectable with a suction space during a suction stroke and during a controlled portion of a delivery stroke of the pump plunger via a fuel duct controlled via an electrically actuated valve, wherein fuel being delivered from a fuel supply tank to the suction space is connectable during the respective delivery stroke of the pump plunger via a distributor opening in a distributor with one of a plurality of pressure ducts.
Such a fuel injection pump is known from DE-OS 37 19 833. In this instance, the pump work space is filled and relieved before the start and after the end of the high-pressure delivery via the fuel duct. The disadvantage of this design consists in that the fuel which is heated beforehand when high pressure is built up in the pump work space and which is controlled via the valve for terminating the high-pressure injection is supplied again to the pump work space during the subsequent suction stroke, at least to the extent that fuel is present in the fuel duct. The temperature of the pump work space accordingly increases, resulting in a high temperature loading of the magnet valve on the one hand and on the other hand in load-dependent and speed-dependent fluctuations in density because the fuel which is taken in varies in temperature. Further, such an increase in temperature in the pump work space leads to greater leakage losses and lower compression pressure due to the reduced filling density, which has a negative effect on the output determined by construction. It is also suggested in DE-OS 36 12 942 generally to cool the valve. This known fuel injection pump has a plurality of pump plungers which define a pump work space. During a suction stroke of the pump plungers the pump work space can be connected with a suction space in which fuel is delivered from a fuel supply tank. During a compression stroke of the pump plungers the pump work space can be connected with one of a number of pressure ducts which are connected via injection lines with the locations where fuel is injected into the internal combustion engine. The pump work space can be connected with a relief space via an electrically controlled valve. The pump plunger stroke effecting the injection is controlled by the valve. Fuel flows out of the suction space, through an interior space of the valve and into the pump work space to cool the valve. When relieved the fuel flows off through a pressure space of the valve. Fuel flows through the interior space of the valve and a cooling of the valve is effected accordingly only during the suction stroke of a pump plunger.